1. Field of the Invention
The present invention relates to a method for controlling a spindle in an optical disc device, and more particularly to a method and apparatus for controlling a maximum rotational speed of an optical disc based on an imbalance error of the optical disc.
2. Description of the Related Art
FIG. 1 is a block diagram of a general optical disc device. For example, a variety of types of optical disc devices such as DVD players may comprise an optical disc 10, an optical pickup 11, an RF processor 12, a digital signal processor 13, a spindle motor 14, a sled motor 15, a microcomputer 16, a motor drive 17, a servo controller 18, and a memory 19 as shown in FIG. 1. The components are operatively coupled.
The optical disc 10 may have a variety of structural errors which cause vibration and noise and exert adverse effects on a servo associated with playback and recording operations. Examples of such errors include an eccentric error caused by mismatch between the center of tracks formed on the optical disc and the center (i.e., a central hole) of the optical disc, and an imbalance error caused when the optical disc is bent asymmetrically in one direction from the center of the disc, e.g., due to the incorrect positioning of the optical disc on the optical disc device.
Generally the eccentric errors exert adverse effects on the servo over a range of low to high disc rotational speeds, almost regardless of the rotational speed of the optical disc. However, generally the imbalance errors exert no noticeable effect on the servo when the spindle motor 14 rotates the optical disc at a low speed while exerting an adverse effect on the servo when the optical disc rotates at a high speed. Thus, the eccentric and imbalance errors are different.
FIG. 2 is a flow chart of a method for controlling a spindle in an optical disc device according to a related art.
When an optical disc 10 is inserted into an optical disc device such as a DVD player, the microcomputer 16 controls the servo controller 18 to perform an operation for setting the maximum spindle/rotational speed of the disc 10.
The microcomputer 16 turns the spindle motor on to rotate the optical disc 10 and turns the focusing servo on while turning the tracking servo off (S10).
The microcomputer 16 rotates the spindle motor 14 at a preset low speed (for example, 3,000 RPM) (S11) and counts track cross signals detected by the optical pickup 11 while the optical disc 10 rotates once at the preset low speed (S12). The track cross signal count represents the number of tracks which a laser beam irradiated by the optical pickup 11 crosses, and corresponds to the eccentric error of the optical disc 10.
The microcomputer 16 compares the number of track crossings counted in the above manner with a first preset reference value (S13). If the track crossing count is equal to or exceeds the first reference value, the microcomputer 16 determines that the optical disc has a large eccentric error and sets the maximum spindle speed of the optical disc to a low spindle speed (for example, ×16) (S17).
On the other hand, if the track crossing count is less than the first reference value, the microcomputer 16 rotates the spindle motor 14 at a preset high speed (for example, 4,300 RPM) (S14) and counts track cross signals detected during one rotation of the optical disc 10 (S15). This track cross signal count corresponds to both the eccentric and imbalance errors of the optical disc 10.
The microcomputer 16 then compares the number of track crossings counted in the above manner with a second preset reference value (S16). If the track count is equal to or exceeds the second reference value, the microcomputer 16 determines that the optical disc has large eccentric and imbalance errors and sets the maximum spindle speed of the optical disc 10 to a low spindle speed (for example, ×16) (S17).
On the other hand, if the track crossing count is less than the second reference value, the microcomputer 16 determines that the optical disc 10 has small eccentric and imbalance errors which are within an acceptable range and thus sets the maximum spindle speed of the optical disc 10 at a high speed (for example, ×32) (S18).
The count of the track cross signals (track crossings) detected when the optical disc rotates at a high speed corresponds to the combination of eccentric and imbalance errors of the optical disc. Thus, for a given disc, if the imbalance error (which exerts an adverse effect only when the optical disc rotates at a high speed) is small and the eccentric error is relatively large, the error (i.e., mostly an eccentric error) detected when the optical disc rotates at a low speed may be larger than the first reference value, but at the same time, an error (i.e., the sum of eccentric and imbalance errors) detected when the optical disc rotates at a high speed is less than the second reference value. In this case, the related art method unnecessarily and unconditionally reduces the maximum spindle speed (S17) based on the eccentric error detected when the optical disc rotates at a low speed, even though the high speed test for the same disc indicates that the maximum spindle speed can and should be maintained.